Tectonic Summary

Seismotectonics of the Middle East and Vicinity

No fewer than four major tectonic plates (Arabia, Eurasia, India, and
Africa) and one smaller tectonic block (Anatolia) are responsible for
seismicity and tectonics in the Middle East and surrounding region.
Geologic development of the region is a consequence of a number of
first-order plate tectonic processes that include subduction,
large-scale transform faulting, compressional mountain building and
crustal extension.

Mountain building in northern Pakistan
and Afghanistan is the result of compressional tectonics associated
with collision of the India plate moving northwards at a rate of 40
mm/yr with respect to the Eurasia plate. Continental thickening of the
northern and western edge of the India subcontinent has produced the
highest mountains in the world, including the Himalayan, Karakoram,
Pamir and Hindu Kush ranges. Earthquake activity and faulting found in
this region, as well as adjacent parts of Afghanistan and India, are
due to collisional plate tectonics.

Beneath the Pamir-Hindu
Kush Mountains of northern Afghanistan, earthquakes occur to depths as
great as 200 km as a result of remnant lithospheric subduction.
Shallower crustal earthquakes in the Pamir-Hindu Mountains occur
primarily along the Main Pamir Thrust and other active Quaternary
faults, which accommodate much of the region's crustal shortening.
The western and eastern margins of the Main Pamir Thrust display a
combination of thrust and strike-slip mechanisms.

Along the
western margin of the Tibetan Plateau, in the vicinity of southeastern
Afghanistan and western Pakistan, the India plate translates obliquely
relative to the Eurasia plate, resulting in a complex fold-and-thrust
belt known as the Sulaiman Range. Faulting in this region includes
strike-slip, reverse-slip and oblique-slip motion and often results in
shallow, destructive earthquakes. The relatively fast moving
left-lateral, strike-slip Chaman Fault system in southeastern
Afghanistan accommodates translational motion between the India and
Eurasia plates. In 1505, a segment of the Chaman Fault system near
Kabul, Afghanistan ruptured causing widespread destruction of Kabul
and surrounding villages. In the same region, the more recent 30 May
1935, M7.6 Quetta, Pakistan earthquake, occurred within the Sulaiman
Range, killing between 30,000 and 60,000 people.

Off the
south coast of Pakistan and southeast coast of Iran, the Makran trench
is the present-day surface expression of active subduction of the
Arabia plate beneath the continental Eurasia plate, which converge at a
rate of approximately 20 mm/yr. Although the Makran subduction zone
has a relatively slow convergence rate, it has produced large
devastating earthquakes and tsunamis. For example, the November 27,
1945 M8.0 mega-thrust earthquake produced a tsunami within the Gulf of
Oman and Arabia Sea, killing over 4,000 people. Northwest of this
active subduction zone, collision of the Arabia and Eurasia plates
forms the approximately 1,500-km-long fold and thrust belt of the
Zagros Mountains, which crosses the whole of western Iran and extends
into northeastern Iraq. Collision of the Arabia and Eurasia plates
also causes crustal shortening in the Alborz Mountains and Kopet Dag
in northern Iran. Eastern Iran experiences destructive earthquakes
that originate on both strike-slip and reverse faults. For example,
the 16 September 1978 M7.8 earthquake, along the southwest edge of the
Dasht-e-Lut Basin killed at least 15,000 people.

Along the
eastern margin of the Mediterranean region there is complex interaction
between the Africa, Arabia and Eurasia plates. The Red Sea Rift is a
spreading center between the Africa and Arabia plates, with a
spreading rate of approximately 10mm/yr near its northern end, and
16mm/yr near its southern end (Chu, D. and Gordon, R. G., 1998).
Seismicity rate and size of earthquakes has been relatively small
along the spreading center, but the rifting process has produced a
series of volcanic systems across western Saudi Arabia.

Further north, the Red Sea Rift terminates at the southern boundary of
the Dead Sea Transform Fault. The Dead Sea Transform is a strike-slip
fault that accommodates differential motion between the Africa and
Arabia plates. Though both the Africa plate, to the west, and the
Arabia plate, to the east, are moving in a NNE direction, the Arabia
plate is moving slightly faster, resulting in the left-lateral,
strike-slip motion along this segment of the plate boundary.
Historically, earthquake activity along the Dead Sea Transform has been
a significant hazard in the densely populated Levant region (eastern
Mediterranean). For example, the November 1759 Near East earthquake is
thought to have killed somewhere between 2,000-20,000 people. The
northern termination of the Dead Sea Transform occurs within a complex
tectonic region of southeast Turkey, where interaction of the Africa
and Arabia plates and the Anatolia block occurs. This involves
translational motion of the Anatolia Block westwards, with a speed of
approximately 25mm/yr with respect to Eurasia, in order to accommodate
closure of the Mediterranean basin.

The right-lateral,
strike-slip North Anatolia Fault, in northern Turkey, accommodates much
of the westwards motion between the Anatolia Block and Eurasia Plate.
Between 1939 and 1999, a series of devastating M7.0+ strike-slip
earthquakes propagated westwards along the North Anatolia Fault
system. The westernmost of these earthquakes was the 17th August 1999,
M7.6 Izmit earthquake, near the Sea of Marmara, killed approximately
17,000 people.

At the southern edge of the Anatolia Block
lies the east-west trending Cyprian Arc with associated levels of
moderate seismicity. The Cyprian Arc represents the convergent boundary
between the Anatolia Block to the north and the Africa Plate to the
south. The boundary is thought to join the East Anatolia Fault zone in
eastern Turkey; however no certain geometry or sense of relative
motion along the entire boundary is widely accepted.

The
August 11, 2012 M 6.4 and M 6.3 earthquakes in northwestern Iran
occurred as a result of oblique strike-slip faulting in the shallow
crust of the Eurasia plate, approximately 300 km east of the plate
boundary between the Eurasia and Arabia plates. The two earthquakes are
separated by just 10 km in an east-west direction. Focal mechanisms,
describing the style of faulting for the earthquakes, suggest slip on
either fault planes striking roughly east-west, or those striking
roughly north-south. Because these earthquakes are intraplate events,
away from the main plate boundary structures in the region, precise
identification of the causative fault(s) is difficult at this time,
though their offset suggest they may be associated with an east-west
striking structure.

On a broad scale, the seismotectonics of this region are controlled
by the collision of the Arabia and Eurasia plates; at the latitude of
the earthquakes, the Arabia plate moves almost due north with respect to
the Eurasia plate at a rate of approximately 26 mm/yr. To the south of
today’s earthquakes, towards Iraq and the Persian Gulf, tectonics are
dominated by the Zagros fold and thrust belt. To the west, in Turkey,
tectonics are dominated by strike-slip faulting on the East (in southern
Turkey) and North (in northern Turkey) Anatolian fault zones,
accommodating the westward motion of the Anatolian block as it is being
squeezed by the converging Arabian and Eurasian plates. The August 11,
2012 earthquakes occurred in the broad, elevated Turkish-Iranian Plateau
region between these regimes and the Alborz Mountains further east. The
events are consistent with the distributed, dominantly strike-slip
mechanisms of historic earthquakes nearby, and with the orientation of
mapped faults in the region.

Over the past 40 years, seven earthquakes of M 6 or greater have
occurred within 300 km of today’s events. The closest was a M 6.1
earthquake in February of 1997, approximately 100 km to the east, which
caused 1100 fatalities. In October of 2011, a M 7.1 earthquake struck
the region of Van in eastern Turkey, near the Iranian border 300 km to
the west of the August 11, 2012 earthquakes, resulting in over 500
fatalities.